Research Objectives and Specific Aims: (1) To isolate and determine the structures of novel antitumor compounds from selected active plant extracts (2) To further modify the selected novel antitumor agents isolated for enhanced activity and reduced toxicity. Research Methods: (1) Extracts of 40 previously unexplored Chinese and North Carolina species in 26 families which have shown potent cytotoxic antileukemic activity against both in vivo growth of P-388 lymphocytic leukemia in mice and in vitro KB tissue culture cell, have been selected for this investigation. (2) Extraction, fractionation and isolation of the active principles will be guided at every stage by an in vitro cytotoxicity assay in KB and P-388. (3) The in vitro-active compounds/fractions will be submitted to National Cancer Institute for in vivo evaluation. (4) Modern physical methods such as UV, IR, PMR, CMR, ORD, CD, mass spectroscopy and x-ray crystallographic analysis as well as elemental analysis will be used to elucidate and confirm the complete structures of the isolated active principles. (5) Studies on structure modification in the course of structural elucidation and synthesis of analogs for the potent antitumor agents with novel structures will be added in order to investigate the structure-activity relationships as well as the possible discovery of new clinically useful anticancer drugs.